Wireless devices for consumer use and the constant trend towards miniaturization demand improvements in microelectronic device packaging and electrical interconnection. For low cost, high volume applications, conventional plastic package technologies are relatively inexpensive and, therefore, attractive. However limitations of bandwidth and isolation render plastic packages generally unsuitable for high frequency applications. The typical maximum usable frequency for a conventional plastic package is about 2 GHz. Package modifications can extend operational frequency, but not much above 4 GHz. Because the signal transmission is horizontal rather than vertical, the frame in a typical plastic package interferes with performance. The package frame contributes significant inductance; as the operational frequency increases, impedance increases. Some plastic packaging provides for a cavity around the IC device, thereby improving performance (See Dozier U.S. Pat. No. 5,428,188). However, performance improvement is constantly sought especially at higher RF and microwave frequencies.
Ceramic based packages are less subject to frame impedance but are typically quite limited in their ability to provide suitable isolation for high frequency applications. Moreover, a ceramic package typically costs around $10 and is, therefore, too expensive for most low cost products. Other packaging technologies all present either cost or performance problems especially with respect to applications designed to operate at high frequencies. Ball Grid Array (BGA) package performance, for example, is subject to serious limitations: difficulty in minimizing the ground and lead inductance; restrictions in design of impedances arising out of manufacturing limitations. Moreover, ground isolation is hampered by the added inductance of the balls in the grid array.
Thus, currently available packaging technologies are not wholly satisfactory for demanding RF, microwave, and millimeter wave applications that require good high frequency performance and low manufacturing cost.